Various types of medical devices have been developed for determining medical information of a subject, e.g., a human. For example, various heart rate detectors are now available for conveniently determining a heart rate of a subject. Some of these medical devices have been made in miniaturized forms, e.g., a portable medical device. In particular, medical devices for determining health information and medical information have been incorporated into various wearable apparatus such as glasses, gloves, watches, apparel, shoes, and hats.